The goal of this project is to understand the biochemical mechanisms controlling assembly of MAGUK-mediated signaling networks. Proper intercellular communication and growth control require establishment and maintenance of supramolecular complexes containing precise networks of signaling pathways and cytoskeletal structure at cell-cell junctions. Scaffolding proteins, such as the membrane-associated guanylate kinase proteins (MAGUKs), are important for assembling these complexes. MAGUKs harbor multiple protein interaction domains that bind receptor, signaling, and cytoskeletal proteins. MAGUKs serve many functions ii cell-cell communication: clustering membrane receptors, coupling receptor activation to specific downstream effectors, and specifying the organization of the supramolecular complexes at cell-cell junctions. I plan to elucidate how MAGUK protein interactions are regulated to permit coordinated complex assembly. Studies o MAGUKs and other signaling proteins suggest interdomain interactions may regulate assembly. Using the PSD-95/DIg/SAP family of MAGUKs as a model, I will combine mutagenic, biochemical, and structural techniques to map/characterize MAGUK regions that modulate ligand binding, either through intramolecular, inter domain interactions or through interactions with regulatory ligands. I will also test a model proposed for oligo. merization between multiple MAGUK proteins, both in vitro and in vivo. These experiments will increase our basic understanding of the mechanisms governing the assembly and function of cell-cell signaling networks.